Anderson's hypothesis had been proved indirectly, but the phenomenon had never been directly observed with particles such as atoms or electrons until recently, when it was witnessed by CNRS researchers Alain Aspect (1) and Philippe Bouyer and their team at the Institut d'Optique (2).
They have, for the first time, shown atoms subjected to minor disorder coming to a complete stop. Published in the June 12, 2008 issue of the journal Nature, these results will make it possible to better understand the role of disorder in the electrical properties of certain materials.
Introducing disorder to certain conducting materials is sometimes enough to make them suddenly become insulating. On our scale, that would be like saying that a few blades of grass scattered haphazardly over a golf course could stop a full-speed golf ball in its tracks. Admittedly, this would a surprising situation, and at our macroscopic scale, small perturbations can slow the movement of material objects, but can never stop them. But this is different at a microscopic level, where matter can also behave like a wave.
In a perfectly ordered solid, an electron moves freely without being disturbed by the underlying regular crystal structure. In disordered solids, however, any flaw will diffuse the matter wave in multiple directions. Combining all these disorder-generated waves can lead to a wave that does not propagate and remains frozen in the crystal.
The electrons (or the atoms) stop their movement, which, in the case of electrons, turns the material into an insulator. Envisioned by Anderson in 1958, this scenario emphasizes the fundamental role of disorder as well as the relevance of studying the electrical properties of disordered materials like amorphous silicon.
In light of the fundamental discoveries made in the 1930s about semi-conductors that led to the invention of the transistor and then to integrated circuits, Anderson's model created strong interest among physicists. While theoretical physicists strived to understand its underlying nature and its significance, experimental physicists tried to observe the phenomenon. Even though convincing experiments existed, direct observation of particle matter located in a weak disorder remained an unattainable goal.
First direct evidence of the Anderson scenario
French researchers at LCFIO took on the challenge by constructing a simple model of the situation that could lead to this phenomenon, called "Anderson localization." In their experiment, ultra-cold (3) atoms play the role of electrons, while the disordered environment is replaced by a perfectly controlled disorder created by light from a laser beam. With the help of a waveguide, the atoms are limited to unidirectional movement. Without disorder, the atoms propagate freely, but when disorder is introduced, all atomic movement stops within a fraction of a second. The researchers then observed the atomic density profile. Its exponential form is characteristic of the scenario envisioned by Anderson (see figure below). By varying the experimental parameters, the researchers were also able to test the theoretical model developed by Laurent Sanchez-Palencia's team at the atomic optics group.
Armed with results obtained from a radically simplified scenario, the physicists at the Institut d'optique now plan on addressing more complex situations in which atoms can move in a plane, or even in the three directions of space. For these conditions approaching those of real materials, theory can not currently precisely predict all situations; experiments alone constitute a type of quantum simulator that can provide part of the answer. Maybe then, by transferring these results to electrons, it will be possible to better define the behavior of these particles in disordered environments. Such results could, in the long run, improve amorphous silicon-based electronic devices, for example.
Used notably in TFT-LCD screens and in some photovoltaic cells, amorphous silicon is significantly less expensive to produce, but currently less effective than the crystalline silicon that forms the base of high performance electronic devices.
(1) CNRS gold medal, 2005.(2) A team at the atomic optics group which is part of the Laboratoire
Julien Guillaume | alfa
Quantum optics allows us to abandon expensive lasers in spectroscopy
22.11.2017 | Lomonosov Moscow State University
Nano-watch has steady hands
22.11.2017 | University of Vienna
The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.
Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
22.11.2017 | Business and Finance
22.11.2017 | Physics and Astronomy
22.11.2017 | Physics and Astronomy